IF we drag our eyes away from our mobile phones and look up we'll notice there are many more solar panels on roofs these days – they are no longer a rarity. I was surprised to read that there are now more than 600,000 houses with them, and that's a useful first step.

Mind you, as there are about 27 million houses in the UK this still only represents marginally over two percent, so about two houses in a street of a hundred, but we couldn't have said that just five years ago. On a recent bus ride around an estate in Cottingley I counted at least twenty roofs adorned with panels, and there were certainly many more I couldn't see.

It's explained by a combination of reasons from the falling price of the panels themselves, and their increasing efficiency, to new forms of installation with householders paying for everything or just renting out their roofs. In the latter case the owner benefits from just meeting his own electricity needs, but in the former they can also sell any surplus into the grid for which they get a guaranteed price, based on a feed in tariff with a twenty five year life. It also helps that most don't need planning permission.

Despite our more northerly latitude ensuring that the sun can never be vertically overhead, there's still enough incoming energy to make solar panels worth while, and this explains the explosion of solar farms, large arrays in fields, that are being developed mainly in the south, though there's even one as far north as Aberdeen.

The proposed farm at Denby Dale, in Kirklees, on old industrial land, will have 7,000 panels and provide the annual electricity for 6,000 homes. It's just one of over 500, with more in the pipeline.

The figures for local properties are very instructive, and the following refers to a normal bungalow in Bradford. It uses solar tiles, rather than panels, and at current prices it would cost less than £5,000 to install. There are also thermal panels to help heat water.

Both systems work to some extent throughout the year, in all the daylight hours, but they are particularly effective on long summer days with sunlight. This means that for about four months of the year there's no need to get any electricity from the grid, and as the surplus is fed back in there's also an income.

The householders report that over the year they produce more electricity than they need and they sensibly use their washing machine and cooker when they are producing their 'free' electricity.

The bonus, of course, is that the use of all this electricity is CO2 free.